The present invention relates to a high-pressure pump for a fuel injection system of an internal combustion engine, in particular for a common rail injection system.
High-pressure pumps for example for common-rail systems are known from the prior art, in which high-pressure pumps a drive shaft is mounted by means of plain bearings which are supplied with pressure and which serve to provide optimum lubrication and cooling. Furthermore, valves which are arranged in series with the bearings in a hydraulic circuit may be arranged downstream of the bearings in order to prevent the flows through the bearings upon start-up.
For example, DE 10 2006 048 356 A1 discloses a high-pressure fuel pump for an internal combustion engine, in which fuel inevitably flows through the bearings of the drive shaft, and as a result the mechanical and thermal load capacity of the bearings and therefore of the entire high-pressure fuel pump is considerably increased. Here, a first and a second plain bearing are provided for mounting the drive shaft. To accelerate the pressure build-up within the high-pressure fuel pump and in the high-pressure accumulator of the common-rail system, a first check valve is arranged downstream of and in series with the first bearing. Correspondingly, a second check valve is arranged downstream of and in series with the second bearing. The opening pressure of the check valves is however selected such that these are closed upon start-up of the internal combustion engine and open only when the internal combustion engine is running
The opening pressure of the check valves used in the prior art lies in a range above 1.0 bar. Said opening pressure is so high that the check valves open only after the suction valves of the high-pressure fuel pump open, such that for example in a start-up situation, no leakage occurs through the bearings, which is however disadvantageous for said bearings.
Also, the pressure on the downstream side of the bearings upstream of the valves increases. If a shaft sealing ring is positioned there, the loading can increase to inadmissible values. For this reason, it is conventionally not possible for a valve to be provided at such bearings.
It is also a disadvantage of the known configurations that, in situations where there is a poor fuel supply, if a mass balance infringement occurs, the high-pressure accumulator continues to be supplied with fuel as before while the valves at the bearings are already closing. The lubrication and cooling of the bearings is in this case no longer ensured.
There is therefore a need to provide a high-pressure fuel pump which can be used in a fuel injection system, in particular in a common-rail system, and in which the mass balance situation is improved in particular upon start-up of the internal combustion engine and which does not have the disadvantages stated above.